Ankylosing spondylitis is a lifelong autoimmune disease — and form of arthritis — that causes inflammation, pain, and stiffness mainly in the spinal joints. Marek Drzazga, Physical Therapist, Total Health Systems

A.S. symptoms vary from person to person. In the early stages of A.S., the pain and stiffness often starts in the lower back, but over time, it may move up the spine and into the neck. Most people with AS experience episodes of acute pain — known as flares — followed by periods when symptoms temporarily subside. For some people, AS can lead to disability and deformity, affecting not just how they feel but also their ability to perform everyday tasks. The disease starts with low back pain that comes and goes. Most common symptoms include: pain and stiffness are worse at night, in the morning, or when you are not active, it may wake you from your sleep, the pain typically gets better with activity or exercise. Back pain may begin in the sacroiliac joints over time, it may involve all or part of the spine. You may lose motion or mobility in the lower spine, you may not be able to fully expand your chest because the joints between the ribs are involved.
There is great importance to exercise for patients of ankylosing spondylitis; it is one of the foundations for managing the pain associated with the condition, and maintaining mobility and strength.
Exercise is an integral part of any spondylitis program. Fitting exercise into your day can be tough, but it needs to be done. Exercise is such a high priority that you must make time for it each day (even 5-10 minutes during a work break is helpful). If you do, many benefits will follow from your efforts. A spondylitis exercise program will help you maintain good posture, flexibility and eventually help to lessen pain.
In many cases, good posture and mobility can even be regained with proper doses of medicine and proper exercise. Most people with spondylitis say they feel much better after exercise.
It is wise to consult your physician about the possibility of you beginning a workout program. We also advise that you find a qualified physical therapist to help you develop an exercise program that will help focus on building proper muscles and diminishing some of the associated pain. The exercise regime from the physical therapist will also help with the postural issues. Learning specific exercises that will help with the mobility, flexibility, and strength of the affected muscles will keep the individual sufferer in a much stronger state to combat this often painful debilitating condition.
In addition to participating in physical therapy, some patients find relief from special support devices. Although they do not help in treating the disease, they may help maintain the posture or position achieved through physical therapy. These include: lumbar supports (e.g., lumbar support pillows), back braces, support mattresses.
References:
http://www.ncbi.nlm.nih.gov
http://ankylosingspondylitisinfo.com
http://www.spine-health.com